Store repository APIs that are being used

They are only stored in memory, thus rebooting James will loose all dinamically generated mail repository (at the very least until they are created again).

To solve this major flow, we need a MailRepositoryUrlStore API (basically a persistant Set<String>) with generic contract tests and memory, cassandra, jpa implementations.

This should be used for MailRepositoryStore::getUrls operation as well as lazyly get repository.

Needs Guice and (ideally) Spring bindings